Blood pump without bearing

ABSTRACT

The blood pump comprises a pump casing ( 10 ) in which an impeller ( 16 ) is installed without any bearing. Said impeller ( 16 ) is rotated via a magnetic coupling ( 32,36 ) by an external magnetic driving means ( 33 ). The impeller is radially centered via the magnetic coupling ( 32,36 ). The lower side ( 30 ) of the blades ( 19 ) of the impeller is configured as supporting surface ( 30 ) sloping towards the trailing end. In this way a hydrodynamical supporting effect is attained during rotation such that the impeller ( 16 ) raises from the bottom surface ( 12 ) of the pump casing ( 10 ). Since no bearings and sealings are provided on the pump casing the danger of thrombosis and the danger of penetration of foreign bodies in the form of abrasive particles into the blood is reduced.

BACKGROUND OF THE INVENTION

The invention relates to a blood pump without bearing, operatingaccording to the rotary pump principle, for temporary or long-term bloodconveyance.

For temporary short-term blood conveyance extracorporeal blood pumps areused which comprise a rotationally driven impeller. Said impeller issupported on bearings in the pump casing. Examples of such blood pumpsare described in EP 0 451 376 B1 and DE 43 21 260 C1. The impeller isdriven via a magnetic coupling by a rotating rotor located outside thepump casing. The bearings supporting the impeller pose a problem inconnection with the blood pump since thrombosis may occur at thebearings. Further, there is the danger of abrasive particles of thebearings contaminating the blood. Seals designed to protect the bearingsagainst penetration of blood have also turned out to be unsuitable forthe medium-term to long-term use (days to years). Blood pumps withmechanical support of the impeller are not suited for the long-term usefor the aforementioned reasons. Pump systems having magnetic bearings(U.S. Pat. No. 5,385,581 A, DE 196 13 388 A1) which contactlesslysupport the impeller in an electromagnetic bearing means require aconsiderable controlling effort and a voluminous configuration becauseof the complex supporting structure where additional energy must besupplied to a large extent due to the active impeller centering.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide a blood pump having a rotorrotating in a pump casing where the danger of blood contamination andthrombosis minimized.

This object is solved according to the invention with the featuresstated in claim 1.

The blood pump according to the invention is a blood pump withoutbearing which is not provided with any mechanical bearings. The impelleris freely movable within a limited clearance in the pump casing. Theimpeller is rotated by an external magnetic driving means thus beingself-centering. At least a front side of the blades comprises supportingsurfaces which hydrodynamically lift the impeller during rotation. Thestatic force of attraction of the permanent magnets in the impeller andthe driving means tends to press the impeller against the pump casingwall facing the driving means. However, the supporting surfaces in theimpeller cause the impeller to be lifted from the bottom surface duringrotation such that the impeller slides on a blood cushion thus beingkept at a distance from the wall. The impeller without bearing ispassively centered in the pump casing via permanent magnets incombination with hydrodynamically acting driving forces. The lateralcentering of the impeller is also effected by the magnets cooperatingwith the driving means. In this way it is possible to create a bloodpump without bearing and shaft where the impeller is suspended in thepump casing.

The blood pump without bearing according to the invention offers theadvantage that due to the fact that no bearings and sliding seals areprovided the risk of thrombosis of the blood and penetration of foreignbodies into the blood is reduced. Thus the blood pump according to theinvention cannot only be used as an extracorporeal blood pump forshort-term application but also as an implantable blood pump forlong-term operation. The blood pump is operable with high efficiency dueto the low centering-induced losses wherein the required capacity liesin the range of 6 W under physiologically relevant operating conditionssuch that the pump has a long service life even when configured as abattery-operated portable device.

The impeller may comprise a straight continuous passage extending fromthe inlet to a bottom wall of the pump casing. Thus the impeller isprovided with vanes on both sides.

Preferably, the impeller blades are arranged such that they protrude toopposite sides from the circumferential wall of a disk-shaped orcone-shaped supporting body. The impeller does not form a disk whichwould, together with the bottom wall of the pump casing, define a narrowgap. This also reduces the risk of thrombosis. In all areas of the pumpcasing a blood flow is maintained without there being the danger of deadwater areas.

As seen from the top the blades are of essentially triangularconfiguration and comprise the blade-side magnets. The triangular formof the blades allows the blade volume to increase with increasing radiussuch that the fluid passage area available between the blades can bekept constant on all radii. Thus the conicality of the pump casing,which would be required to ensure that on all circumferential circlesapproximately the same volume is available, is reduced or eliminated.

The blood pump according to the invention is a centrifugal pump wherethe outlet is arranged essentially tangentially to the outer edge of thepump casing. Since the maximum pressure prevails in the outlet a radialforce is produced which tends to press the impeller away from theoutlet. To counteract this decentering force a peripheral ring diffusoris provided on the pump casing according to a preferred aspect of theinvention, the ring diffusor ending in a tangential outlet. Said ringdiffusor is a helical duct which causes the pressure prevailing in theoutlet to be distributed over the circumference of the pump casing thushaving a centering effect on the impeller.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereunder embodiments of the invention are explained in detail withreference to the drawings in which:

FIG. 1 shows a schematic longitudinal section across a first embodimentof the blood pump,

FIG. 2 shows a perspective view of the pump casing of the blood pumpshown in FIG. 1,

FIG. 3 shows a view of the impeller of the pump shown in FIG. 1,

FIG. 4 shows another perspective view of the impeller of the pump shownin FIG. 1,

FIG. 5 shows a second embodiment of the blood pump,

FIG. 6 shows a perspective view of the pump casing of the pump shown inFIG. 5,

FIG. 7 shows a perspective view of the impeller of the pump shown inFIG. 5,

FIG. 8 shows a third embodiment of the blood pump,

FIG. 9 shows the pump casing of the blood pump shown in FIG. 8, and

FIG. 10 shows the impeller of the blood pump shown in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

The blood pump shown in FIG. 1 comprises a pump casing 10 having atruncated circumferential wall 11, an essentially flat bottom wall 12and a peripheral cylindrical wall 13 extending between said bottom wall12 and said circumferential wall 11. The blood is supplied via the axialinlet 14 to the pump casing and leaves the latter via the tangentialoutlet 15 on the outer casing circumference.

In the pump casing 10 an impeller 16 is rotatably arranged. Saidimpeller comprises a truncated supporting body 17 whose slope isapproximately half as large as that of the circumferential wall 11. Thesupporting body 17 is made of surface material of approximatelyidentical thickness at all locations. On the supporting body 17 blades18,19 protruding to the top and to the bottom are arranged wherein theupper blades 18 and the lower blades 19 are congruent as seen from thetop, i.e. they have the same projection surfaces.

Said blades 18,19 are of triangular configuration as seen from the topand comprise a convex circumferential surface 20 coinciding with thecircumferential circle of the supporting body 17, a convex leadingsurface 21 leading in the direction of rotation, and a concave innersurface 22. Said convex leading surface 21 coincides with the concaveinner surface 22 at the inner edge 23. The circle on, which lie theinner edges 23 of the three blade pairs, form the limit of a circularpassage 24 arranged in axial extension of the inlet 14. This means thatthe impeller 16 is open in its center such that a direct axial passage24 extends down to the bottom wall 12 wherein a central raised portion25 extending into said passage 24 is provided in the bottom wall 12. Thecross-section of the passage 24 is at least as large as that of theinlet 14.

When the impeller rotates, the respective inner edge 23 precedes theouter edge 26 of the same leading surface 21. This means that theleading surface 21 presses the medium radially to the outside by settingsaid medium into a swirling motion. The trailing edge 27 moves along thesame path as the leading edge 26.

The upper side 28 of the upper blades 18 moves in a truncated planehaving the same cone angle as the circumferential surface 11 of the pumpcasing. Between the upper sides 28 of the blades and the conicalcircumferential surface 11 of the pump casing a gap is formed whichprovides the play required for axial movement of the impeller.

The lower sides of the lower blades 19 form supporting surfaces 30 whichlift the impeller from the bottom wall 12 of the pump casing when theimpeller rotates in the direction indicated by arrow 31. Said supportingfaces are formed in that on the lower side of the blade the lower edgeof the leding surface 21 is positioned at a larger distance to thebottom wall 12 than at the trailing end, namely at the edge 27. In thisway a gap is formed between the supporting surface 30 and the bottomwall 12, the gap decreasing towards the trailing end such that fluid inthe gap tends to lift the impeller. Further, the vertical height of thegap above the bottom wall increases from the inner edge 23 towards theoutside whereby the impeller is also radially centered. The inclinationangle α of the supporting surface 30 in the circumferential direction isapproximately 2 to 40°.

The blades 18,19 which are of triangular configuration as seen from thetop are each provided with a magnet 32 with north pole N and south poleS. Said magnet extends through the two blades 18,19.

The blood pump is driven by an external magnetic driving means 33 ontowhich the pump casing 10 is placed. Said driving means comprises a rotor34 supported in bearings 35 and being provided with magnets 36 on itscircumference. Each of said magnets 36 attracts a magnet 32 located inthe pump casing 10. The rotor 34 is rotated by stationary electromagnets37. Each electromagnet 37 comprises a U-shaped yoke through which passesa magnet 38 arranged on the circumference of the rotor 34. The poles ofthe electromagnets 37 are cyclically changed such that they generate arotating magnetic field carrying along the rotor 34. Via themagnetically coupled magnets 32 and 36 the rotor 34 rotates the impeller16. All parts of the impeller 16, with the exception of the magnets 32,are made of plastic material or another nonmagnetic material.

The type of magnet arrangement of the rotor magnet 32 at the drivemagnet 36 results in a radial centering of the impeller 16. Thus 2cartesian axes and 3 rotating axes are defined. The last remainingdegree of freedom in the direction of magnetic attraction is fixed bythe convergent gap formed between the supporting wall 30 and the bottomwall 12 and extending in circumferential direction. Thus the impeller,when rotating, raises from the bottom wall 12 against the magneticattraction. When a sufficient circumferential velocity of the impellerhas been reached, a blood film capable of bearing forms in theconvergent gap and the impeller is suspended in the pump casing withoutmixed friction.

In the embodiment shown in FIG. 5 the casing 10 a comprises a flatbottom wall 11 and a flat upper wall 11 a extending essentially inparallel to the former. The supporting body 17 a, from which the blades18,19 protrude to the top and to the bottom, is a flat disk.

According to FIG. 5 the external driving means 33 a compriseselectromagnets 40 distributed on the circumference of the pump casing 10a and generating a peripheral magnetic field. The yokes of theelectromagnets 40 directly act upon the magnets 32 of the impeller 16 a.Here, too, the magnets do not only carry out the rotary drive of theimpeller but also its radial centering. For axial centering of theimpeller the blades are provided with an inclined supporting surface 30on their lower side and with an inclined supporting surface 41 on theirupper side, said supporting surfaces forming, together with the upperwall 11 a of the pump casing, a convergent centering gap.

The blades 18,19 have the blade form shown in FIG. 7 deviating from thatof the first embodiment in that the vanes are curved in forwarddirection as seen in the direction of rotation. In all cases the bladesextend up to the passage 24 and the blade width (in circumferentialdirection) increases from the passage 24 towards the outside such thateach blade has its maximum width at the edge of the supporting body 17and 17 a, respectively. According to FIG. 6 the pump casing 10 agenerally has the form of a flat cylinder with a flat upper wall 11 aand a cylindrical circumferential wall 13. Since during rotation of theimpeller 16 a the maximum pressure builds up in the outlet 15 it mayhappen that this pressure presses the impeller against the pump casingside located opposite to the outlet. To compensate for this pressureforce a ring diffusor 44 extends around the circumference of the pumpcasing, said ring diffusor 44 completely enclosing the circumference ofthe pump casing and being configured as a helical bulge whosecross-section continuously enlarges from the inlet end 44 a towards theoutlet 15.

The embodiment shown in FIGS. 8 to 10 corresponds to a large extent tothat shown in FIGS. 5 to 7. The pump casing 10 b is essentiallyconfigured as a flat cylinder with a flat upper side 11 a and a flatbottom wall 12. The lower side of the lower blades 19 forms ahydrodynamical supporting surface 30 which increases, as in the previousembodiments, towards the leading edge. Further, the supporting surface30 shown in FIG. 8 increases towards the outside.

The driving means 33 b comprises a disk rotor motor 45 supported inbearings 35 and being provided with magnets 36 which cooperate with themagnets 32 of the impeller 16 b.

What is claimed is:
 1. A blood pump without bearing, having a pump casing comprising an axial inlet and an outlet disposed on its circumference, and having an impeller rotatably arranged in said pump casing, said impeller being provided with magnets adapted to cooperate with an external magnetic driving means, wherein the impeller is freely movable within a limited clearance in the pump casing, and the blades on the lower side of the impeller facing the driving means comprise hydrodynamically lifting support surfaces, characterized in that, as seen from the top, the blades are of essentially triangular configuration, wherein the blade width increases with increasing radius and wherein the blades have a convex outer surface on the circular border of a supporting body.
 2. A blood pump comprising: a housing including an axial inlet and tangential outlet on its circumference, and upper and lower surfaces substantially parallel to one another; an impeller floating freely within said housing without bearing when rotating therein about an axis of rotation, the impeller comprising a disc-shaped support body and a plurality of blades supported on the support body, the blades having a magnet disposed therein and hydrodynamic lifting surfaces on a lower surface thereof; and a magnetic drive external to the housing, said magnetic drive system cooperating with the magnets disposed on the blades of the impeller to bias the impeller to rotate about its axis of rotation.
 3. The blood pump of claim 2 wherein the blades on the impeller have a triangular configuration when viewed from above and including a leading surface, a trailing surface, a leading edge at an outer radius, a trailing edge at an outer radius, and a coincident leading edge and trailing edge at an inner radius, where the leading edge at the outer radius precedes the leading edge at the inner radius in the direction of rotation of the impeller.
 4. The blood pump of claim 2 wherein the disk-shaped support body extends substantially to a cylindrical wall of the housing.
 5. A blood pump comprising: a housing including an axial inlet and tangential outlet on its circumference; an impeller floating freely within said housing without bearing when rotating therein about an axis of rotation, the impeller comprising a support body and a plurality of blades supported on the support body, the blades having a magnet disposed therein and hydrodynamic lifting surfaces on a lower surface thereof, the blades further comprising a triangular configuration when viewed from above and including a leading surface, a trailing surface, a leading edge at an outer radius of the leading surface, a trailing edge at an outer radius of the trailing surface, and a coincident leading edge and trailing edge at an inner radius where the leading surface and trailing surface converges, a space between the leading surface of a first blade and a trailing surface of an adjacent blade defining a blood flow passage, the blades configured such that the blood flow passage area between successive blades is constant for all radii on the impeller; and a magnetic drive external to the housing, said magnetic drive system cooperating with the magnets disposed on the blades of the impeller to bias the impeller to rotate about its axis of rotation.
 6. The blood pump of claim 5 wherein the impeller comprises three blades.
 7. The blood pump of claim 5 wherein the support body is coextensive with the outer radius of the impeller.
 8. The blood pump of claim 5 wherein the housing is substantially cylindrical.
 9. The blood pump of claim 5 wherein the housing is substantially conical.
 10. The blood pump of claim 5 wherein the leading edge at the inner radius precedes the leading edge at the outer radius in the direction of rotation of the impeller.
 11. The blood pump of claim 5 wherein the leading edge at the outer radius precedes the leading edge at the inner radius in the direction of rotation of the impeller.
 12. The blood pump of claim 5 wherein the magnetic drive comprises a drive rotor rotating about the impeller axis of rotation, the drive rotor comprising magnets aligned with said magnets on the blades of the impeller for driving the impeller within the housing. 